Paracrine Engineering of Human Cardiac Stem Cells to Over-Express Stromal Cell-Derived Factor 1 alpha Enhances Post-Ischemic Cardiac Repair

Introduction: First generation cardiac stem cell (CSC) products provide indirect cardiac repair but variably produce key cardioprotective cytokines (such as stromal-cell derived factor 1α (SDF1α)) which opens the prospect of maximizing up-front paracrine-mediated repair. Methods/Results: The mesenchymal sub-population within human CSCs underwent lentiviral (lv) mediated gene transfer of SDF1α. Cytokine array profiling revealed that SDF1α over-expression prevented lv-mediated “loss of cytokines” through autocrine stimulation of the 47±4% CXCR4+ CSCs. SDF1α enhanced angiogenesis and stem cell recruitment while priming CSCs to readily adopt a cardiac identity. As compared to injection with unmodified CSCs, transplant of SDF1α transduced CSCs into NOD SCID mice improved myocardial function (4 week LVEF: 39±2 vs. 33±1%; p≤0.05) and angiogenesis (4±0.7 vs. 2±0.5 isolectin b4+ve vessels/field; p≤0.05) while reducing scarring (4.0±0.2 vs. 5.8±0.7%, p≤0.05). Infarct, infarct border and off-target regions demonstrated greater SDF1α content (7 days post injection: 51±12, 7±1 and 16±5 fold increased vs. unmodified CSCs, p≤0.05) which paralleled reductions in myocyte apoptosis (i.e., increased Bcl-2 to Bax ratio disparity) but did not influence long-term CSC engraftment or the fate of transplanted cells. BrdU pulsing revealed that transplantation of SDF1α transduced CSCs increased the generation of new myocytes (BrdU+/TnT+; 1.4±0.1 fold increase vs. unmodified CSCs; p=0.02). A murine sex mismatch bone marrow transplant model confirmed that transplant of unmodified CSCs did not increase recruitment of bone marrow cells (vs. PBS injection alone) while transplant of SDF1α transduced CSCs increased bone marrow cell recruitment by 2.3±0.5 and 1.5±0.3 fold at 7 (p≤0.05) and 14 (p=0.08) days after CSC injection as compared to transplant of unmodified CSCs. Conclusions: Paracrine engineering of human CSCs to over-express SDF1α enhances recruitment of endogenous stem cells, new myocyte/vessel formation and salvage of reversibly damaged myocardium to enhance cardiac repair after experimental MI.